1. Field of the Invention
The present invention relate to a recording device used as an output device of an ink-jet recording apparatus exerting recordation by discharging an ink from a recording unit to a recording medium, and an apparatus having such a function, e.g., a facsimile, a duplicator, a printer multifunction machine and a workstation.
2. Description of the Related Art
In recent years, color documents have been widely spread in office use, and various kinds of output apparatuses have been proposed therefor. In particular, an ink-jet system, which can be miniaturized with low cost, is used in various kinds of output apparatuses.
A recording head used in the ink-jet system is constituted with an energy generating unit, an energy converting unit for converting energy generated by the energy generating unit to an ink discharging force, an ink discharging outlet for discharging an ink droplet with the ink discharging force, and an ink feeding path connected to the ink discharging outlet for feeding an ink. Examples of the energy generating unit include devices using an electromechanical converting element, such as a piezoelectric element, and devices, in which an ink is heated with an electrothermal conversion element having a resistive heater element to form a bubble, and the ink is discharged with the formation of the bubble.
In the recording head utilizing an electrothermal conversion element, not only ink discharging outlets can be arranged at a high density owing to the small size of the electrothermal conversion element, but also a production technique of a semiconductor integrated circuit can be transferred for the production technique therefor. Accordingly, a recording head having a large number of ink discharging outlets can be miniaturized and can be produced at low cost.
However, what has been commonly used is a printing system referred to as a serial scanning system, in which a recording head is reciprocally moved with recording paper being conveyed to print by one line. While the system is of a small size and low cost, it has such a problem in that the printing speed is low due to necessity of plural frequencies of scanning of the recording head for forming an image over the paper. It is necessary to lower the scanning frequency in order to improve the printing speed, and extension of a recording head is essential therefor. At the outrance of the extension of a recording head, such a non-scanning printing system is proposed in that a recording head having the same width as recording paper is used. The printing system uses an ink-jet recording apparatus having a recording head having a width equivalent to recording paper, within which a large number of discharging outlets are arranged over the length, which is substantially the same as the recording paper, and recordation is effected by moving the recording paper with respect to the fixed recording head.
In order to improve the productivity, such a recording apparatus capable of printing over the paper width have been thus proposed that has a long recording head having a width equivalent to the maximum paper width of the recording paper and carries out printing with the paper being conveyed. It has been known that the recording head capable of printing over the paper width is not only constituted with a monolithic long recording head having a length equivalent to the paper width but also constituted by arranging short heads in a staggered manner or by arranging them with the ends thereof being in contact with each other.
In the ink-jet recording apparatus, an ink droplet discharged from a nozzle of the recording head flies and impacts on the paper to form an image. At this time, because the discharging velocity of the ink droplet is generally constant, fluctuation in the flying distance (i.e., the distance between the recording head (nozzle surface) and the paper) causes fluctuation in the impact position of the ink droplet, which directly influences the quality of the image thus formed.
In the conventional recording apparatus having a scanning type recording head, accordingly, the distance between the recording head and the paper is generally uniformized in such a manner that the paper is intermittently conveyed and is exactly fixed on a platen at the printing position.
In the case of printing over the paper width, on the other hand, the paper is continuously conveyed by using a belt, a drum or the like, and therefore, an electrostatic adsorption system, a negative pressure adsorption system or the like is used as a uniformizing system for maintaining uniform the distance between the nozzle surface and the paper.
For example, as a system for uniformizing at the printing position, such methods have been proposed as a method of electrostatically adsorbing paper on a platen (as described, for example, in JP-A-2-225232), a method of aspirating paper by negative pressure (as described, for example, in JP-A-10-157229), and the like.
However, it has been well known in the art that paper is swelled and deformed at a part, at which an ink is attached, to cause ununiform deformation over the entire paper, and the surface potential and the conveying resistance (friction coefficient) thereof are also changed. The extents of the deformation and the changes greatly depend on the quality and the thickness of the paper.
In the conventional technique using the electrostatic adsorption and the negative pressure aspiration, it has been confirmed that deformation of the paper caused by penetration of an ink due to change in surface potential cannot be avoided, and a part of the paper is left from the conveying members (such as a belt and a drum) during printing. Accordingly, it is difficult to maintain uniform the distance between the nozzle surface of the recording head arranged over the paper width and the paper.
In the case where the paper is conveyed with a belt, furthermore, there is such a possibility that the distance between the nozzle head of the recording head and the paper is changed by vertical movement of the belt, such as vibration. Moreover, there is also such a possibility that the tip end part of the paper is deformed in the vertical direction upon conveying due to against wind (i.e., air resistance) to change the distance to the nozzle surface of the recording head.
As a result, the distance between the recording head (nozzle surface) and the paper is changed to differentiate the flight time of the ink droplets, whereby the image quality is deteriorated.